Guitar Amp is built according to the original Fender schematic. The amp has a built-in vibrato effect achieved by a low-frequency oscillator. This effect can be switched on and off by an external pedal. Tubes used are 12AX7, 6V6, and 5Y3. Output power is about 6 watts into 3.2 ohms. Fender replacement transformers were used for building this circuit.

Schematic Circuit Amplifier
The total description of the amplifier is given in Figs 6 and 7 and Table 8 (in datasheet). The amplifiers input and output matching networks contain mixed microstrip-lumped elements networks to transform the terminal impedance levels to approx. 25 W balanced. The remaining transformation to 50 W unbalanced is obtained by 1 : 2 balun transformers. The baluns B1 and B2 are 25 W semi-rigid coax cables with an electrical length of 45° at midband and a diameter of 1.8 mm, soldered over the whole length on top of microstrip lines.

To keep the circuit in balance two stubs L1 and L8 with the same length have been added. For low frequency stability enhancement the input balun stubs are connected to the bias point by means of 1 W series resistors. Large capacitors (C4 and C11) are added at the biasing points to improve the amplifiers video response.

This Printed Circuit Board (PCB)
The printed-circuit board laminate utilised is PTFE-glass with an er = 2.55 and a thickness of 0.51 mm (20 mills).

Component Mounted

A complete TV transmitter amplifier has been designed and characterised based on the BLV861, capable of operating in full band IV and V with flat gain and high output power in class-AB. BLV861 is able to generate 100 W CW power and a power gain compression below 1 dB in band IV and V. Overall gain of the amplifier is >8.5 dB and an efficiency of ± 55%. TV-measurements have been carried out showing a 1 dB compression point above 120 W PO, SYNC at VCE = 28 V
and 150 W at VCE = 32 V.

* Amplifier shows an agreed linearity performance in class AB operation both under two tone and three tone conditions
* Biasing the amplifier at a VCE = 32 V results in a higher output peak sync power and a better linearity response.

The TV amplifier has been tuned under class-A small-signal conditions and characterised under large signal class-AB conditions from 470 - 860 MHz. (All Datasheets) DOWNLOAD HERE

This can in fact be accomplished with a single chip - the BA1404, or the newer NJM2035. But I say - why do it with one chip when you can use five? :) ( - or four chips, if you use the dual version of the opamp - the CA3240).

Seriously, this circuit works well as the sender end of a wireless headphone solution, in conjunction with a personal FM radio. The power is sufficient to service the author's house, though stereo loss occurs if I venture off down the garden. Alternatively, it can be used to hear various MP3 players, iPods, etc. on the car radio, where there is rarely a facility for external input.

The circuit just fitted into a case with integral 9V battery compartment (the sort that comes with a clip so that you can attach it to your belt, pocket, etc. though I didn't use this). Externally, the case has just a switch, a short lead to a 3.5mm stereo jack plug, and a two foot length of aerial cable. A small hole is drilled to allow access to the tuning trimmer without having to open the case.

All capacitors around the transmitter section must be ceramic. Leads must be kept short here. A self-supporting coil is used (because it's cheap), but to stop 'twangs' being transmitted when the case of the unit is bumped, the whole transmitter area, including the coil, was caked in candle wax. One must, of course, leave the trimmer accessible for tuning purposes.

If you have the equipment to set this circuit up precisely, then I probably don't need to explain how to do it! Set-up can be accomplished without any equipment, provided a stereo signal source is available, and a stereo FM radio with headphones connected (headphones will enable you to easily hear when stereo sound is being decoded).

The set-up procedure is roughly as follows:

1. Adjust the transmitter section tuning trimmer to place the sender's signal in a an empty part of the FM dial (if such a space can be found these days!).

2. A good starting point for the Pilot tone level pot is about 30% of setting.

3. Apply power and connect the stereo sound source to the circuit. Set the modulation level pot to minimum for the moment (i.e. maximum resistance).

4. Listening with the stereo radio, adjust the 76kHz frequency pot until the (albeit quiet) received signal suddenly resolves into stereo. This may be indicated on the radio by a 'Stereo' LED illuminating. Ensure that the radio is able to lock and resolve stereo every time by tuning it to another station momentarily, and then returning it to the sender's signal. You will find there is a range of settings of the frequency pot over which stereo can be obtained reliably. When the bounds of this range have been determined, set the 76kHz frequency pot to the centre of this range.

5. If stereo cannot be obtained at all by these methods, try repeating your efforts after increasing the Pilot tone level pot a little.

6. Finally, adjust the Modulation level pot so that the received sound has the same subjective volume as the commercial stations on the dial. It might be best to set the pot a little lower than this, as commercial FM stations are often subjected to compression so that they appear louder for a given modulation limit.

The Modulation level pot enables the circuit to be adapted to the particular level on the 'Line out' socket provided of most CD players, etc. If it is intended to connect several devices at different times, then it may prove necessary to use the headphone socket in each case, so that the volume control can then be used as a modulation level control instead.

FM radio employs 'treble pre-emphasis' by which signal frequencies above a certain frequency are lifted, so as to overcome noise. The 'time constant' emplyed for this purpose differs from country to country. In the US this time constant is 75us. In the UK it is 50us. It will be necessary to select an appropriate resistor in the opamp circuits so that the required pre-emphasis in your country is applied. Suitable values for the UK and US are given in the circuit.

Do make sure you don't annoy neighbours by jamming their favourite station! These circuits are not illegal in many countries so long as they do not interfere with legitimate services. Regardless of their legality, remember that you might just need that neighbour's help one day, and he may be less inclined to give it if you've ruined his favourite classical listening!

Finally, the 10mA current drain allows some fifty hours of use from a duracell battery. If a shorter range can be tolerated (e.g. if the circuit is only ever used in the car where the circuit can be sited close to the radio aerial), then greater economy can be achieved by increasing the emitter resistor (1k) in the transmitter circuit.

This circuit is similar to the 6V6 Amp except that it has two channels. It puts out about 10 watts into 8, 4, or 2 ohms. Tubes used are 6SN7, 6V6, and 5U4. Negative feedback is taken off the output transformer's secondary.

WARNING!

Tube circuitry uses lethal amounts of current at high voltages. Be extremely careful when constructing any types of tube circuitry. Here are some tips for building circuits safely:

When testing circuits, do not stand on metal or anything grounded.

When measuring voltages in the circuit, use only one hand.

Never work on a circuit while it is plugged in.

Discharge filter capacitors through a resistor after turning off the circuit.

Wait for tubes to cool before handling or removing.

Use common sense and don't do anything stupid.

Note: I am not responsible for injury or death as a result of carelessness in the construction of the circuits on this site.

These two power amplifiers are almost identical except for the brand of power transformer. Tubes used are 6BM8 and 6X4. Output power is about 3 watts into 8 ohms. The output pentode is connected to a 40% ultra-linear tap on the output transformer.

WARNING!

Tube circuitry uses lethal amounts of current at high voltages. Be extremely careful when constructing any types of tube circuitry. Here are some tips for building circuits safely:

When testing circuits, do not stand on metal or anything grounded.

When measuring voltages in the circuit, use only one hand.

Never work on a circuit while it is plugged in.

Discharge filter capacitors through a resistor after turning off the circuit.

Wait for tubes to cool before handling or removing.

Use common sense and don't do anything stupid.

Note: I am not responsible for injury or death as a result of carelessness in the construction of the circuits on this site.